On December 29, 2014, Entergy shut down its Vermont Yankee nuclear facility after 42 years in service. Located in southeast Vermont along the Connecticut River, Vermont Yankee was a 604 megawatt boiling water reactor that began commercial operation in 1972. It has generated nearly five million megawatt hours of electricity per year since 2010, accounting for 4% of New England's total electric generation and over 70% of generation in the state of Vermont in that time period.

Entergy submitted its Post-Shutdown Decommissioning Activities Report and the Site-Specific Decommissioning Cost Estimate to the U.S. Nuclear Regulatory Commission on December 23, 2014. The decommissioning process is lengthy and can take decades to fully complete dismantling, decontamination, and site restoration activities. Entergy currently estimates total decommissioning costs of more than $1.2 billion. These costs include $817 million for license termination (a broad category encompassing costs such as labor, equipment, and materials, and the removal of plant systems and components), $368 million for spent fuel management and $57 million for site restoration.

With the closure of Vermont Yankee, there are now 99 nuclear units in the United States with a combined summer nameplate capacity of 98,620 megawatts. New England has dealt with the closure of nuclear units before, with the retirement of the 560 megawatt Connecticut Yankee unit in 1996 and the 870 megawatt Maine Yankee in 1997. Four nuclear units are currently active in New England: Millstone 2 and 3 in Connecticut, Pilgrim Nuclear Power Station in Massachusetts and Seabrook in New Hampshire. These units have a combined summer nameplate capacity of 4,026 megawatts and had an average capacity factor of just over 90% in 2014 (through October).

The nearly five million megawatt hours of generation historically produced at Vermont Yankee per year can be replaced in several ways. Existing generators in New England can operate at higher rates. New England's generation is dominated by natural gas and nuclear units, which combined for 77% of ISONE generation in 2014. As the four existing nuclear units already operate at maximum capacity and renewable sources generate power on a variable basis, the additional generation would come largely from natural gas, coal, or petroleum-fueled units.

Source: U.S. Energy Information Administration, based on ISO New England

New England could also import more electricity along its existing transmission ties to neighboring electricity grids. The Independent System Operator of New England (ISONE) has interconnections to Canada and New York and consistently imports several thousand megawatts of electricity each hour along those lines. These electricity imports met 14% of New England's demand in 2013, according to ISONE.

Source: U.S. Energy Information Administration, based on ISO New England

Transmission capacity into New England could also be expanded. The Northern Maine Independent System Administrator (NMISA) traditionally has had more generating capacity than needed and is isolated from the rest of New England, with ties only to Canada. NMISA is currently considering ways to access the New England electrical grid directly, which would bring additional generating capacity into the New England market. Hydro-Quebec is also in the approval process with its Northern Pass transmission project. If constructed, Northern Pass would have the potential to bring up to 1,200 megawatts of electricity into New England.

Electricity demand and demand growth could also be lowered through increased energy efficiency and demand response programs to counteract the retirement of generating units. ISONE currently counts 2,100 megawatts of demand resources (load management, distributed generation and energy-efficiency programs) and expects this number to increase in the coming years.